The present invention is related to non-destructive inspection techniques to perform real time quality control of, in particular, but not limited to, fiber composite material manufacturing processes, out-of-autoclave curing processes and conventional processes such as autoclave. More in particular, the invention relates to a new technique based on an ultrasonic inspection system.
Most composite material parts manufactured today for the aeronautics industry are traditionally made according to autoclave curing processes. The main weaknesses of this technology include:
The inevitable heavy investment not only due to all the necessary equipment but also due to all the infrastructure associated with the autoclave process (space necessary, installation, tools, auxiliary materials, power consumption, maintenance, etc.);
The need of having a large enough autoclave to house the part to be manufactured, which clearly imposes a limitation on the design of the parts to be manufactured, reducing manufacturing flexibility; and
The reduced process energy yield making the composite material parts manufactured according to this curing technology more expensive.
Among the options considered to overcome these drawbacks would be the use of alternative technologies for curing/reticulating the resin without the need of autoclave. Some of these technologies are electron beam curing, microwave curing, radiofrequency curing and induction curing. Each of these technologies has its advantages and drawbacks as well as its degree of maturity for different applications, and all of them have in common the elimination of the autoclave for the final curing of the part. Based on the need for a non-destructive inspection of the composite parts, and particularly parts manufactured according to the new processes, it is obvious that these new processes must be provided with a solution/an inspection technology which is capable of being adapted to the specific requirements of these processes, but which in turn maintain at least the capacities of the current systems for inspecting autoclave manufactured parts. The current non-destructive ultrasound testing techniques (NDT) perform quality control on the part once the part has been made and the material is completely cured.
NDTs have been used for decades to detect material and structural defects. The basic idea is simple: an electronic system excites an ultrasonic transducer generating a high frequency mechanical wave pulse which is introduced and propagates in the material to be inspected. When the ultrasonic pulse finds a heterogeneity inside the material, part of the incident energy is reflected in the form of an echo which returns to the transducer, where the vibrations are converted again into electrical signals. After amplification, the echoes indicate the presence of a defect, its position and size estimation.
These techniques have been greatly developed and have many applications in different industrial areas. They are particularly indispensable in the fields of aeronautics, energy generation, oil prospecting, rail transport and public works in which the verification of structure and part safety margins is an obligation and is performed with NDT techniques. Likewise, most manufacturing industries (metallurgy, automobile, machine-tool, etc.) use NDT techniques to assure the quality of their products.
The NDT systems have often been automated by associating them with robots that mechanically scan the parts to assure the structural integrity throughout their dimension.
Technology advancements over the past few years in the field of electronics and ultrasound transduction technologies have allowed performing inspections with a never before seen precision and speed. Currently the state of the art of the technology allows constructing very complex electronic systems from tens to several hundreds of channels, this is possible as a result of the mass integration of hardware processing functions provided by the technology.
The ultrasonic array-based technology facilitates arbitrary deflection and focusing of the ultrasonic beam in emission and reception without the need of moving or altering the transducer by means of an electronic control. The composition of the traces received allows constructing 2D and 3D images of the inside of the inspected materials. In fact, ultrasound has been used in medicine for almost three centuries with remarkable success.
Since the market appearance of the first successful system of NDT with arrays [FOCUS-TomoScan©, by Rd Tech, Canada] in 1996, this technology is being demanded by a growing number of users in different industrial sectors since the advantages it provides compensate its high cost.
One of the problems limiting the applicability of the inspection by means of ultrasounds on carbon fiber parts is the need of coupling the transducers to the materials. Due to the large acoustic impedance differences, great insertion losses occur between emission and reception if a suitable coupling means is not available. This is solved by, for instance, performing complete or partial immersions using water jets or micro-troughs, which is a cumbersome procedure, as in EP1914544A2, or need water films in contact with the material to be inspected to ultrasonically couple the transducer with such material.